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        // 3. 请描述下面代码的输出结果以及运行原因

        //    ```js

        // 先提升变量还有函数
        // 提出变量
        var num

        function demo() {
            var num
            function demoSon() {
                console.log(num);
                //  2

                num = 3;
                console.log(num);
                // 3
            }
            console.log(num);
            //  undefined 

            num = 2
            demoSon();
        }
        demo();







        var num;
        
        function demo() {
            var num;
           
            function demoSon() {
                console.log(num);
                num = 3;
                console.log(num);
            }
            console.log(num);
            num = 2
            demoSon();
        }
        num = 1;
        demo();






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